The number of American teens who wind up in the emergency room after taking Ecstasy has more than doubled in recent years.

Emergency room visits related to MDMA -- or Ecstasy and Molly -- increased 128 percent between 2005 and 2011 among people younger than 21. Visits rose from about 4,500 to more than 10,000 during that time.

Ecstasy produces feelings of increased energy and euphoria, and can distort a person's senses and perception of time. It works by altering the brain's chemistry, but research hasn't been able to come up with the effects of long-term abuse on the brain.

Ecstasy abuse can cause potentially harmful physical reactions. People can become

dangerously overheated and experience rapid heartbeat, increased blood pressure and dehydration, all of which can lead to kidney or heart failure.

Alcohol also appears to be a factor. One-third of the emergency room visits involving Ecstasy also involved alcohol, a combination that can cause a longer-lasting euphoria. Teens can become less aware of how much alcohol they've consumed, and also can be more likely to make poor decisions that lead to bodily harm.

MDMA affects a person's level of serotonin, a hormone that helps regulate sleep cycles and is responsible for feelings of happiness and well-being. Overusing the drug can cause depression, confusion, paranoia, anxiety and sleep disorders.